CHEM 1110 Lecture Notes - Lecture 6: Freezing-Point Depression, Boiling-Point Elevation, Osmotic Pressure

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yellowhippopotamus301

7 Feb 2017

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Document Summary

Entropy gain from solid to liquid is smaller for pure solvent. Higher in solution than in pure solvent. Difference is directly prop to molal concentration. Proportionality is called bp elevation constant: kb. Difference between fp of solution and solvent is prop to molal concentration of. Sugar cant come out but water can go in: cherry burst. Osmotic pressure directly prop to molarity of solute particles. Colloidal suspension: hetero mixture where one substance is dispersed, not dissolved through another substance. Most are finely divided particles suspended in a medium. Difference between colloids and suspensions (settling occurs): particle size. Colloidal particles are 1 to 1000 nm in size. Nonpolar tail and ionic head: forms micelle. How much quantity changes in a given period of time. Average speed: total distance over total time. Ave rate: measured change in concentration of a reactant or product. Reactants: negative sign in front of definition: reactant concentrations fall. Slope of plot of concentration vs time.

Related Questions

Â± Boiling Point Elevation and Freezing Point Depression for Organic Solutions

The temperature at which a solution freezes and boils depends on the freezing and boiling points of the pure solvent as well as on the molal concentration of particles (molecules and ions) in the solution. For nonvolatile solutes, the boiling point of the solution is higher than that of the pure solvent and the freezing point is lower. The change in the boiling for a solution, ÎTb, can be calculated as

ÎTb=Kbâ m

in which m is the molality of the solution and Kb is the molal boiling-point-elevation constant for the solvent. The freezing-point depression, ÎTf, can be calculated in a similar manner:

ÎTf=Kfâ m

in which m is the molality of the solution and Kf is the molal freezing-point-depression constant for the solvent.

Part A

Cyclohexane has a freezing point of 6.50 âC and a Kf of 20.0 âC/m. What is the freezing point of a solution made by dissolving 0.463 g of biphenyl (C12H10) in 25.0 g of cyclohexane?

Express the temperature numerically in degrees Celsius.

Part B

Paradichlorobenzene, C6H4Cl2, is a component of mothballs. A solution of 2.00 g in 22.5 g of cyclohexane boils at 82.39 âC. The boiling point of pure cyclohexane is 80.70 âC. Calculate Kb for cyclohexane.

Express the constant numerically in degrees Celsius per molal.